This invention is directed to novel collagen compositions and to methods of using such compositions. In particular, the collagen compositions of this invention are directed to oxidized collagen compositions wherein the thiomethyl group of one or more of the methionine residues of the collagen has been replaced with methylsulfoxy and/or methylsulfonyl groups.
Surprisingly, the oxidized collagen compositions described herein are compatible with pharmaceutical drugs which are otherwise non-compatible with non-oxidized collagen. Accordingly, the oxidized collagen compositions described herein provide for improved drug delivery, administration, clinical utility and/or therapeutic use of certain non-compatible pharmaceutical drugs, particularly cytotoxic drugs, when used in combination with the oxidized collagen. In addition, the oxidized collagen compositions described herein will provide for improved drug delivery when used with compatible pharmaceutical drugs.
The following publications are cited in this application as superscript numbers:
1 Southard, et al., Drug Delivery Devices, U.S. Pat. No. 5,013,553 issued on May 7, 1991
2 Luck, et al., Treatments Employing Drug-Containing Matrices for Introduction into Cellular Lesion Areas, U.S. Pat. No. 4,619,913, issued Oct. 28, 1986
3 Jones, et al., Translucent Collagen Formulations with a Cytotoxic Drug, U.S. Pat. No. 5,750,146, issued May 12, 1998
All of the above references are herein incorporated by reference in their entirety to the same extent as if each individual reference was specifically and individually indicated to be incorporated herein by reference in its entirety.
Collagen is a well known biomaterial having many uses in medicine, including, for example, use as a hemostat, use in soft tissue augmentation, use for treatment of urinary incontinence, and use as a drug delivery platform. Examples of use of collagen as a drug delivery platform include collagen compositions comprising a benzo(c)phenanthridine alkaloid or a cytotoxic drug.1,2 
Collagen can be formulated with, for example, cytotoxic drugs, where the collagen is used as a drug delivery device to locally administer the drug to a patient while minimizing systemic uptake.2,3 In certain instances, the drug is compatible with the collagen for only a limited period of time and subsequently becomes non-compatible with the collagen, thereby inhibiting the effectiveness of the preparation and often adversely affecting its administration to the patient. Without being limited to any theory, it is believed that this non-compatiblity arises by undesirable reactions, such as cross-linking, between the non-compatible drug and the collagen chains. Cisplatin, for example, has a tendency to react with protein, nucleic acid, and other substances with nucleophilic groups. When cisplatin is combined into an aqueous collagen gel, the resulting preparation becomes progressively, over time, more rigid and inhomogeneous, and cisplatin recovery is decreased. It is further believed that the cisplatin reacts with nucleophilic groups in the collagen resulting in collagen cross-linking.
In affecting the ability to form physically and chemically stable collagen-based formulations, such reactions both impair the therapeutic activity of the non-compatible pharmaceutical drug and change the rheologic characteristics of the preparation, making the material variable in efficacy and difficult to administer.
Because of this non-compatibility, it is necessary to mix cisplatin with the collagen composition just prior to administration, and to complete the administration within several hours after mixing.
In one embodiment, this invention is directed to the discovery that oxidation of the thiomethyl group in one or more methionine residues in collagen to the corresponding methylsulfoxy or methylsulfonyl group renders the resulting collagen composition more compatible with otherwise non-compatible drugs. In this regard, collagen generally exists as long, rod-shaped molecules that are comprised of a triple helix formed as either a homo- or heterotrimer from three polypeptide chains. The primary structure is characterized by glycine-X-Y repeats, where a significant number of the X""s are proline or hydroxyproline and Y comprises other amino acid residues, including methionine and histidine residues. At physiological pH, the individual collagen molecules self-assemble into microscopic or macroscopic fibrils or networks, which provide the typical extracellular matrix scaffolding exhibited by collagen. When collagen is used in drug delivery applications, fibrillar collagen can act as a thickening agent in aqueous systems, providing a viscous gel-like material. Collagen can also be dried into pellet-like forms for use in sustained-release implants.
Many pharmaceutical drugs are believed to be non-compatible for use with collagen formulations because they contain functional groups that, over time, can participate in undesirable reactions with collagen, e.g., they can react with the methionine residues of collagen. These undesirable reactions can result in cross-linking between the non-compatible drug and the collagen chains. As noted above, such cross-linking significantly impairs the effectiveness of the collagen/pharmaceutical drug composition.
This invention relates to oxidized collagen compositions wherein the thiomethyl group of one or more of the methionine residues of the collagen is replaced by methylsulfoxy and/or methylsulfonyl groups. As noted above, such compositions have improved compatibility with cytotoxic drugs such as cisplatin which drugs are otherwise non-compatible upon prolonged contact with the collagen.
Accordingly, in one of its composition aspects, this invention is directed to oxidized collagen wherein the thiomethyl group of one or more of the methionine residues of the collagen have been replaced by methylsulfoxy and/or methylsulfonyl groups.
Preferably, at least 20% of the methionine residues of the collagen have been replaced by methylsulfoxy and/or methylsulfonyl groups. More preferably, at least 40% and still more preferably at least 60% of the methionine residues of the collagen have been replaced by methylsulfoxy and/or methylsulfonyl groups.
This invention is also directed to the discovery that replacement of one or more of the methionine residues in collagen with methylsulfoxy and/or methylsulfonyl groups prior to addition of a non-compatible pharmaceutical drug reduces or prevents undesirable reactions, such as cross-linking, between the non-compatible drug and collagen thereby rendering the non-compatible drug more compatible with collagen. Without being limited to any theory, it is believed that replacement of methionine thiomethyl groups by methylsulfoxy and/or methylsulfonyl groups reduces or prevents reactions between the sulfur nucleophile in the methionine and non-compatible drugs. Also surprisingly and unexpectedly, this replacement does not substantially affect the ability of the collagen molecules to form fibrils and, accordingly, does not affect the properties of the collagen to act as a carrier for the pharmaceutical drug.
In addition, such a reduction in undesirable reactions also permits formulations comprising compatible drugs which, in some cases, may provide for one or more improved features such as improved shelf-life, improved efficacy, and the like.
Accordingly, in another of its composition aspects, this invention is directed to a pharmaceutical composition comprising:
a) oxidized collagen wherein the thiomethyl group of one or more of the methionine residues of the collagen have been replaced by methylsulfoxy and/or methylsulfonyl groups; and
b) a pharmaceutical drug.
The pharmaceutical drug employed in these compositions can either be compatible or non-compatible with non-oxidized collagen. However, the benefits of oxidized collagen are most pronounced when the drug is otherwise non-compatible with non-oxidized collagen. Preferably, the pharmaceutical drug is a cytotoxic drug and more preferably is a platinate.
This invention is also directed to the discovery that undesirable reactions between collagen and non-compatible pharmaceutical drugs are reduced when the formulation is acidified, i.e, when the pH of the formulation is lowered to less than about 4.5 (e.g., to pH 3.7) and more preferably from about 2.5 to 4.5. It is believed that acidification of the collagen formulation protonates histidine residues in collagen reversing, reducing or preventing reactions between histidine residues and non-compatible drugs. It has been found that the benefits of acidification can be achieved either by acidification of the collagen formulation prior to or after the addition of a non-compatible drug.
It has been still further found that undesirable reactions between collagen and non-compatible pharmaceutical drugs are reduced when the concentration of collagen used in the formulation is reduced. Preferably, the amount of collagen in the formulation is about 3% w/w or lower and more preferably from about 1% w/w to about 3% w/w.
The benefits of acidification of the collagen composition in combination with the pharmaceutical drug is achieved either alone or in combination with use of oxidized collagen. Accordingly, in another of its composition aspects, this invention is directed to a pharmaceutical composition comprising collagen and a pharmaceutical drug wherein the pH of said composition is less than about 4.5. Preferably, the pH of the composition is from about 2.5 to about 4.5 and more preferably is about 3.7.
In another preferred embodiment, the collagen employed in the acidified collagen composition is oxidized collagen as described herein.
In one of its method aspects, this invention is directed to a method for rendering non-compatible drugs compatible with collagen which method comprises replacing one or more of the collagen""s methionine thiomethyl groups with methylsulfoxy and/or methylsulfonyl groups. In one embodiment, this replacement may be achieved by contacting a collagen composition with an oxidizing agent under conditions wherein one or more of the collagen""s methionine thiomethyl groups are converted to methylsulfoxy and/or methylsulfonyl groups. Suitable oxidizing agents are well known in the art and preferably include hydrogen peroxide, meta-chloro perbenzoic acid, and the like.
Alternatively, oxidized collagen wherein one or more of the collagen""s methionine thiomethyl groups are replaced with methylsulfoxy and/or methylsulfonyl groups can be prepared by routine protein chemistry. For example, standard solid phase synthesis can be used to insert an oxidized methionine residue in place of the methionine residue into the growing peptide.
The method described above may further include lowering the pH of the collagen composition to less than or equal to 3.7; and/or lowering the concentration of the collagen in the formulation to about 3% w/w or lower.
In another of its method aspects, this invention is directed to a method for treating neoplastic lesions or surrounding tissue which method comprises introducing at the site of the lesion or tissue surrounding the lesion a pharmaceutical composition comprising:
(a) a collagen composition selected from the group consisting of oxidized collagen, collagen acidified to a pH of from about 2.5 to about 4.5, and oxidized collagen acidified to a pH of from about 2.5 to about 4.5; and
(b) a pharmaceutically acceptable cytotoxic drug.